There are many applications in which it is desired to detect the presence and, preferably the concentration of harmful substances even low-level, in a fluid. By way of example and not limitation, it may be desired to detect the presence and concentration of a microbial pathogen in a source of drinking water such as, for example, a lake, reservoir, river, stream, storage tank, water main, or well. Some harmful substances may be difficult to detect using conventional methods at lower concentrations. For instance, certain microbial pathogens may be harmful to human health at concentrations that are too low to accurately, reliably, and economically detect using conventional methods. Furthermore, in some situations, the sample size used in conventional detection methods may not provide testing results that reflect the actual concentration in the source from which the sample was obtained with an acceptable level of accuracy or certainty. For example, the concentration of a microbial pathogen in a few milliliters of water taken from a source of drinking water may not accurately represent the actual average concentration of the microbial pathogen in that source. As a result, analysis of multiple samples from a single fluid source may be required to determine the concentration of a harmful substance in the fluid source with an acceptable level of certainty.
For each of the above reasons, it has been proposed in the art to concentrate a fluid sample taken from a fluid source by a known concentration factor prior to determining the concentration of a harmful substance in the concentrated fluid sample. Once the concentration of the harmful substance in the concentrated fluid sample has been determined, the concentration in the unconcentrated fluid sample can be determined using the known concentration factor by which the fluid sample was concentrated.
As one example, it may be desired to know the concentration of a particular microbial pathogen in a source. A relatively large sample of water (e.g., about 100 liters) may be taken from the source. Some of the water may be separated or removed from the relatively large sample of water without separating or removing any significant number of the microbial pathogens of interest to provide a relatively smaller concentrated sample (e.g., about 1 liter) that includes substantially all of the microbial pathogens in the original relatively large sample of water. The identity and concentration of the microbial pathogens in the relatively smaller concentrated sample then may be determined, and the known identity and concentration of these pathogens in the concentrated sample may be used to determine the concentration in the original unconcentrated sample of water and, hence, the approximate concentration in the source.
Such methods may result in relatively higher concentrations of the harmful substance in the concentrated sample that are more readily detectible using conventional analytical techniques than if these analytical techniques were used to attempt to detect these harmful substances at the concentrations in the unconcentrated sample, and may result in measurements that more accurately reflect the actual presence and concentration of the harmful substance in the fluid source from which the sample was obtained for analysis.
There remains a need in the art for systems and methods that are portable, automated, that provide accurate and repeatable measurements, that provide acceptable concentration factors in acceptable amounts of time, and that minimize or reduce the risk of exposure of an operator to any harmful substance potentially carried by the fluid sample.